A display device that includes a non-self-emissive display panel such as a transmissive liquid crystal display panel generally includes a light source device that is disposed behind the display panel (also referred to as a “backlight device”). The light source device included in the display device is capable of illuminating the back surface of the display panel with light. When the back surface of the display panel is illuminated with the light, an image is displayed visible on the front surface of the display panel.
Examples of the light source device that is used in the display device include a direct light source device and a side-edge light source device. Among them, the direct light source device includes, for example, a chassis having the shape of a tray of low height, a light source such as a fluorescent tube, an optical member having a plate shape that is arranged to control the properties of light transmitted therethrough, optical members that are more deformable than the plate-shaped optical member (e.g., optical members having a sheet or film shape that are thinner than the plate-shaped optical member), a frame having a substantially square shape with an opening, and other predetermined members. The plate-shaped optical member, and the sheet-shaped or film-shaped optical members are also referred to as optical sheets.
In the light source device, the light source is disposed in front of the chassis, and the plate-shaped optical member and the sheet-shaped or film-shaped optical members are disposed in front of the chassis and the light source. The frame is attached to a front surface of the chassis while the light source, the plate-shaped optical member and the sheet-shaped or film-shaped optical members are disposed in front of the chassis.
Thus, a border portion of the plate-shaped optical member is sandwiched between a front surface of the chassis and a back surface of the frame, whereby the plate-shaped optical member is held in the light source device. The sheet-shaped or film-shaped optical members are layered on the front surface of the plate-shaped optical member. The light source device having the configuration described above is arranged to control the properties of the light emitted from the light source with the use of the optical members, and to illuminate the back surface of the display panel with the light the optical members transmit.
It is preferable that the plate-shaped optical member and the sheet-shaped or film-shaped optical members are supported such that no wrinkle or no distortion occurs therein. If a wrinkle or distortion occurs in these optical members, intensity distribution in a plane direction of the light emitting toward the back surface of the display panel could be nonuniform. The nonuniform intensity distribution in the plane direction of the emitted light could produce luminance unevenness or shadow on a screen of the display panel. The luminance unevenness or shadow could lower display quality of the display device. That is the reason why it is preferable that the optical members are supported such that no wrinkle or no distortion occurs therein.
During the use of the light source device, heat liberated by the light source could cause the optical members to expand. Having the above-described configuration that its border portion is in contact with or stuck between the front surface of the chassis and the back surface of the frame, the plate-shaped optical member has the border portion hindered from deforming, whereby a wrinkle or distortion could occur in the vicinity of the border portion, or the border portion could bend overall. Hence, in order that the border portion of the plate-shaped optical member may not be fixed, the clearance between the front surface of the chassis and the back surface of the frame is increased in size more than the thickness of the plate-shaped optical member (in using a plurality of plate-shaped optical members, more than the sum of their thicknesses). Consequently, the border portion of the plate-shaped optical member is not hindered from deforming, which can prevent a wrinkle or distortion from occurring in the plate-shaped optical member, or the plate-shaped optical member from bending.
However, because this configuration forms a clearance between the plate-shaped optical member and the back surface of the frame, a border portion of the sheet-shaped or film-shaped optical members that are disposed in front of the plate-shaped optical member could get into the formed clearance and get fixed therein. In such a case, an unexpected force could be exerted on the sheet-shaped or film-shaped optical members, causing a wrinkle or distortion to occur therein. In addition, when heat liberated by the light source could cause the sheet-shaped or film-shaped optical members in the fixed state to expand, a wrinkle or distortion could occur in the vicinity of the border portion.
In order that the border portion of the sheet-shaped or film-shaped optical members may not get into the clearance between the plate-shaped optical member and the back surface of the frame, the clearance between the plate-shaped optical member and the back surface of the frame may be decreased in size less than the thickness of the sheet-shaped or film-shaped optical members. However, the sheet-shaped or film-shaped optical members, the plate-shaped optical member or the frame is sometimes deformed elastically to get into the clearance. Getting into and being stuck in the clearance between the plate-shaped optical member and the frame, the border portion of the sheet-shaped or film-shaped optical members is hindered from deforming, causing a wrinkle or distortion to occur in the vicinity of the border portion of the sheet-shaped or film-shaped optical members.
As described above, it is difficult to prevent a wrinkle or distortion from occurring in the sheet-shaped or film-shaped optical members while preventing a wrinkle or distortion from occurring in the plate-shaped optical member in the light source device having the configurations described above. In other words, when a plurality of optical members are used, it is difficult to prevent a wrinkle or distortion from occurring in an optical member while preventing a wrinkle or distortion from occurring in another optical member.